(CNN) -- Marathon man John Isner survived another epic on his return to competitive tennis after his record-breaking 11-hour Wimbledon match.
The American saved two match points before beating Gilles Muller, from Luxembourg, 4-6 7-6 7-6 to seal his place in the quarterfinals of the Atlanta Tennis Championships.
It is Isner's first tournament since Wimbledon back in June when his opening round victory over Frenchman Nicolas Mahut in London clocked in as the longest match in tennis history.
Isner's battle with Mahut stretched over three days and 183 games before he finally triumphed, 6-4 3-6 6-7 7-6 70-68. He later told CNN: "I really didn't think it was going to end."
The match turned Isner into a household name in the sport, and after his straight sets defeat to Thiemo de Bakker in the second round the 25-year-old targeted a prolonged period of rest.
But on his return to the court he was made to work hard by Muller, saving two match points and firing 33 aces as he won in two-and-a-half hours to delight the 5,000 strong crowd.
"I didn't want to let [the fans] down," Isner told the ATP tour website. "I didn't want to lose my first match here. Also, I had a lot of friends and family here, so I didn't want to go out early.
"I hadn't seen a live ball in quite some time and Gilles was never going to give me rhythm with his lefty serve. I felt I was shedding the rust off in the second and third sets. I will only keep getting better.
"As a tennis player you need a lot of matches to play your best. This was one of the biggest wins of the year. I wanted to get matches under my belt before D.C. and the two Masters 1000s."
Isner was catapulted to a new level of fame after his marathon match but the world number 19 insists he wants to be remembered for more than just a first-round Wimbledon victory.
"I'm ranked in the top 20, I think I can still improve and keep climbing," he said. "My goal is to reach the top 10 and contend at the really big events.
"The match was pretty ugly to be honest, but I was proud how I competed and the crowd helped in that regard.
"I was down break points a couple of times in the second set -- they were kind of baby match points with the way he was serving."
Isner will now face fellow American Michael Russell in the last eight.